According to JIS P 0001 “Paper, board and pulp—Vocabulary”, greaseproof paper is defined as follows: 1) A general term for paper endowed with grease resistance; and 2) Paper or board having very high resistance to penetration of grease or fat.
In packaging materials for food products etc., greaseproof paper endowed with grease resistance is widely used. Particularly, for food products such as chocolates, pizzas, and donuts which contain large amount of grease or fat components, greaseproof paper is used so as to prevent grease from penetrating into the packaging materials. If grease or fat components contained in the food product penetrate into the packaging material, there is a possibility that grease penetrates up to the packaging material's surface that is not in contact with the food product, resulting in formation of grease stain which may deteriorate the appearance and thus commercial value of the product, may blacken a printed portion to make characters illegible, or may reduce the suitability of a barcode or the like for OCR. Since there is also the problem that grease is transferred to and smirches clothes, greaseproof paper is used which is endowed with grease resistance at a portion that comes into contact with a food product.
In order for greaseproof paper to exhibit grease resistance, fluorine compounds, particularly fluorinated compounds containing a perfluoro group, have been conventionally used. However, fluorinated compounds containing a perfluoro group have caused safety concerns because it has been revealed that when subjected to heating treatment, they produce substances that will accumulate in and do harm to human bodies. Under these circumstances, greaseproof paper has been proposed in which the surface of a paper base is coated with a fluorine-free greaseproof agent as an alternative to fluorine compounds.
It is known that vinyl alcohol polymers (“vinyl alcohol polymer” may be abbreviated as “PVA” hereinafter) can be used as fluorine-free greaseproof agents. PVAs are hydrophilic resins and form a strong film; therefore, they can prevent penetration of grease and are excellent in grease resistance. For example, Patent Literature 1 proposes greaseproof paper coated with a coating agent in which a PVA or a combination of a PVA and a crosslinking agent is used, and Patent Literature 2 proposes greaseproof paper coated with a coating agent containing starch and/or a PVA and a fatty acid. In either case, however, there is a problem in that grease resistance is significantly degraded and reduced particularly when the paper is folded.